Impact of active calls on available call slots in a shared line appearance

Answered Question
Dec 1st, 2008

Since we have to prepare for the migration of our traditional PBX to an VoIP infrastructure we just started gathering basic knowledge on VoIP communication principles and product specific features. Since we do not have access to an test environment we completely rely on official documentation or on comments of experienced users.


Topic:

I am trying to understand the impact of active calls and calls on hold on the number of available call slots of phones participation in a shared line appearance.


Question:

Does an active call or a call on hold reduce the number of available call slots on all phones participating in a shard line or only on the phone which executes the call?


Let's consider two phones using both a shared line (line 1 with DN 1). The settings of both phones is as follows :

Phone 1: Max_number-of-Calls: 2; Busy trigger: 2

Phone 2: Max_number-of-Calls: 1; Busy trigger: 1

Let's assume one active call on phone 1. Phone 2 then displays the status “remote in use” for the shared line (line 1). Does the status “remote in use” occupy the only available call slot on phone 2 or is this call slot still available for other calls?

What about a call on hold, is the behavior of a caal on hold regarding the occupied call slots in a shared lien appearance similar or different to an active call?


Best regards

Eckhard



Correct Answer by Rob Huffman about 8 years 2 months ago

Hi Eckhard,


It seems you have a better grasp of this than the document we were looking at :)


I just tried this exact setup in the lab and when this scenario is tested only phone 3 is ringing on the second call. Both 1 & 2 are unavailable to take the new call.


I think the best way to go here is to follow the Cisco "best practice"


Cisco recommends that the same value be configured for the maximum number of calls for all shared-line MCID devices.


Hope this helps!

Rob



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Rob Huffman Mon, 12/01/2008 - 06:05

Hi Eckhard,


This is discussed nicely in this clip from a section all about Shared Lines;


The following example demonstrates how three Cisco Unified IP Phones with the same shared-line appearance, directory number 2000, use Call Forward Busy Trigger and Maximum Number of Calls settings. This example assumes that two calls occur. The following values configuration applies for the devices:


-Cisco Unified IP Phone 1-Configured for a maximum call value of 1 and busy trigger value of 1


-Cisco Unified IP Phone 2-Configured for a maximum call value of 1 and busy trigger value of 1


-Cisco Unified IP Phone 3-Configured a for maximum call value of 2 and busy trigger value of 2


When Cisco Unified IP Phone User 1 dials directory number 2000 for the first call, all three devices ring. The user for the Cisco Unified IP Phone 3 picks up the call, and the Cisco Unified IP Phones 1 and 2 go to remote in use. When the user for Cisco Unified IP Phone 3 puts the call on hold, user can retrieve the call from the Cisco Unified IP Phone 1 or Cisco Unified IP Phone 2. When User 2 dials directory number 2000 for the second call, only Cisco Unified IP Phone 2 and Cisco Unified IP Phone 3 ring.


From this good doc;


http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/admin/6_0_1/ccmsys/a03dn.html#wp1100362


Hope this helps!

Rob

eckhard.steinmetz Mon, 12/01/2008 - 21:18

Hi Rob,


many thanks for the link to the document you quoted in your response.


Indeed, this description is very helpful but it seems to contradict with the contents of a second paragraph you will find in the same document some sections later:


A shared-line phone should not be able to interact with the call that it rejects, due to the limitation of the maximum number of calls per DN or for other reasons. For example, A and A1 share the same DN. A1 and A have the maximum number of calls set to 1 and 2, respectively. When C and D call the share line DN, A1 answers these two calls. A can only interact with the first call, as it rejects the second call due to its own maximum number of calls per DN limitation. For this reason, Cisco recommends that the same value be configured for the maximum number of calls for all shared-line MCID devices.


Based on the explanations given above, I'm wondering why in the scenario you quoted in your mail both phones, Phone 2 and Phone 3, should respond to a second call. I would expect that only Phone 3 is ringing when a second call arrives at the shared line. According to the explanations given above, Phone 2 should be occupied through the “remote in use” call of Phone 1.


It seems to me that the documentation isn't consistent or I haven't got the idea behind both scenarios described in the doc you mentioned in your response.


Do you have an idea?


Eckhard

Correct Answer
Rob Huffman Tue, 12/02/2008 - 06:45

Hi Eckhard,


It seems you have a better grasp of this than the document we were looking at :)


I just tried this exact setup in the lab and when this scenario is tested only phone 3 is ringing on the second call. Both 1 & 2 are unavailable to take the new call.


I think the best way to go here is to follow the Cisco "best practice"


Cisco recommends that the same value be configured for the maximum number of calls for all shared-line MCID devices.


Hope this helps!

Rob



Rob Huffman Wed, 12/03/2008 - 06:21

Hi Eckhard,


You are most welcome my friend! Great job sorting through these docs to determine the actual functionality.


Cheers!

Rob

seaman0555 Thu, 12/04/2008 - 10:34

We have found that you will get additional calls to a set with it has the max number set higher. This can really cause problems if you want to put that call on hold and have someone else pick it up since it does not exist on their set.

Rob Huffman Thu, 01/15/2009 - 06:34

Hi Eckhard,


Just thought that I would follow up and let you know that the docs will be changed to reflect the correct workings like you nicely noted and we proved in our testing :)


CSCsq49585 Bug Details


Documentation about shared lines and busy trigger incorrect

Symptom:


Incorrect Information on shared lines and busy trigger in the "Understanding Directory Numbers" chapter in the Cisco Unified CM System Guide/online hlep


Information in the guide/online help is as follows:


Devices with shared-line appearance support the Call Forward Busy Trigger and the Maximum Number of Calls settings. You can configure Call Forward Busy Trigger per line appearance, but the configuration cannot exceed the maximum number call setting for that directory number.

The following example demonstrates how three Cisco Unified IP Phones with the same shared-line appearance, directory number 2000, use Call Forward Busy Trigger and Maximum Number of Calls settings. This example assumes that two calls occur. The following values configuration applies for the devices:


* Cisco Unified IP Phone 1-Configured for a maximum call value of 1 and busy trigger value of 1

* Cisco Unified IP Phone 2-Configured for a maximum call value of 1 and busy trigger value of 1

* Cisco Unified IP Phone 3-Configured a for maximum call value of 2 and busy trigger value of 2


When Cisco Unified IP Phone User 1 dials directory number 2000 for the first call, all three devices ring. The user for the Cisco Unified IP Phone 3 picks up the call, and the Cisco Unified IP Phones 1 and 2 go to remote in use. When the user for Cisco Unified IP Phone 3 puts the call on hold, user can retrieve the call from the Cisco Unified IP Phone 1 or Cisco Unified IP Phone 2. When User 2 dials directory number 2000 for the second call, only Cisco Unified IP Phone 2 and Cisco Unified IP Phone 3 ring.


Incorrect statement in the guide: "When User 2 dials directory number 2000 for the second call, only Cisco Unified IP Phone 2 and Cisco Unified IP Phone 3 ring."


Conditions:


Cisco Unified CM


Workaround:


The documentation should state that only phone 3 should ring as the busy trigger of Phone 1 and 2 (set to 1) has been hit Status

Fixed


Severity

4 - minor


Last Modified

In Last Year


Product

Cisco Unified Communications Manager (CallManager)


Technology



1st Found-In

7.0(0)


Fixed-In

Release-Pending



Rock On!

Rob

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